Traction systems for lifts or elevators are known per se. Ropes, but also belts, are frequently used as pulling means, with both flat belts and V-ribbed belts or even toothed belts being used as belts.
Where ropes are used as pulling means, each individual rope is clearly assigned a dedicated rope groove on the traction sheave. In this arrangement, each rope penetrates with at least part of the diameter thereof into the associated rope groove.
Each individual rope is an independent tension element and can also be operated individually. For higher power requirements, it is possible to use either a plurality of ropes in parallel or for the rope diameter to be increased accordingly. The individual rope is thus not only a pulling means for transmitting the pulling forces but also participates directly in the transmission of the traction forces.
Compared with belt systems, ropes afford the advantage that the force can be transmitted directly from the traction sheave to the ropes. In the case of belt systems, there is, in addition, the connecting elastomer material between the actual tension members and the traction sheave.
Where belts are used, a plurality of adjacent ropes as tension elements is always embedded in a common belt body. Here, the tension elements are completely encased by the base material of the belt body, and the plane of the tension elements is above the contact plane formed by the belt with the corresponding belt sheave, it being possible to consider the belt toothing as the contact plane in the case of toothed belts, the plane of the V as the contact plane in the case of V ribs, and the flat belt surface itself as the contact plane in the case of flat belts.
The tension elements are thus exclusively responsible for transmitting the pulling forces. For higher power requirements, wider belts or belts belonging to a higher power category with a larger belt pitch and stronger tension elements can be used.
Fundamentally, the width of the belts is significantly greater than the height thereof in order to ensure that they run in a stable manner on the sheave.
EP 1 396 458 A2 describes an elevator device in which a flat belt made of elastomer material reinforced with strength members is used as a pulling means. U.S. Pat. No. 7,757,817 B2 shows an elevator having a V-ribbed belt.
Compared with ropes, belts offer the advantage, on the one hand, that handling is simpler since it is not necessary to lay individual ropes onto corresponding grooves of the traction sheave and that even small traction sheave diameters can be employed without problems since the embedded tension members generally have relatively small diameters. Moreover, belts as pulling means are virtually maintenance-free since no lubrication is required.
However, the force that can be transmitted is dependent not only on the friction between the traction sheave and the elastomer but also on how well the tension members are embedded in the elastomer, that is, on the adhesion between the elastomer and the tension member and on the shear strength of the elastomer.
Moreover, at least two and, in general, three to five belts must always be used in parallel in lifts, for example, for safety reasons. The fact that the belts contain a large number of thin individual ropes makes them relatively wide in comparison with a rope of the same strength. If a plurality of belts is now used in parallel, relatively wide traction sheaves and deflection sheaves are required.
U.S. Pat. No. 6,739,433 discloses a tension member for an elevator which is designed as a profiled flat belt, thus somewhat increasing the size of the surface available for friction between the traction sheave and the belt. The force that can be transmitted is thus somewhat greater than in the case of an unprofiled flat belt but, here too, the zone of force transmission between the traction sheave and the pulling means is still a significant distance from the tension members, with the result that the elastomer material of the flat belt is subjected to relatively severe shear stress.